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A multi-spectral photodetector for detecting two or more different bands of infrared radiation is described. The photodetector includes a diffractive resonant optical cavity that resonates at the two or more infrared radiation bands of interest. By detecting infrared radiation at two or more discret

A multi-spectral photodetector for detecting two or more different bands of infrared radiation is described. The photodetector includes a diffractive resonant optical cavity that resonates at the two or more infrared radiation bands of interest. By detecting infrared radiation at two or more discrete applied biases and by generating a spectral response curve for the photodetector at each of these biases, the response to each of the individual bands of infrared radiation can be calculated. The response to each band of infrared radiation can be found by deconvolving the response at each bias. The photodetector finds many uses including military and medical imaging applications and can cover a broad portion of the infrared spectrum.

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1. A multi-spectral infrared radiation photodetector comprising:a plurality of elongate infrared radiation absorbing elements for absorbing at least two bands of infrared radiation, each of the plurality of elements having first and second opposite longitudinal surfaces, the at least two bands of in

1. A multi-spectral infrared radiation photodetector comprising:a plurality of elongate infrared radiation absorbing elements for absorbing at least two bands of infrared radiation, each of the plurality of elements having first and second opposite longitudinal surfaces, the at least two bands of infrared radiation incident upon the first surfaces of the plurality of elements; a plurality of electrically interconnected strips respectively being in electrical contact with and extending along the first surfaces of the plurality of elements; a bottom contact being in electrical contact with the second surfaces of the plurality of elements, the plurality of strips and the bottom contact to provide for current flow through the plurality of elements in a direction substantially transverse to an axis of the plurality of elements; and a reflector for the at least two bands of infrared radiation, the reflector being disposed on an opposite longitudinal surface of the bottom contact from the plurality of elements, wherein the plurality of elements, the plurality of strips, the bottom contact and the reflector comprise a diffractive resonant optical cavity for the at least two bands of infrared radiation, and wherein a ratio between a photoresponse to each of the at least two bands of infrared radiation is a function of an external bias applied between the plurality of strips and the bottom contact. 2. A multi-spectral infrared radiation photodetector in accordance with claim 1, wherein the plurality of elements comprise multiple quantum well material selected from the group consisting of GaAs, AlGaAs, InGaAs, InP and combinations thereof.3. A multi-spectral infrared radiation photodetector in accordance with claim 1, wherein the reflector is either a metallic reflector or a Bragg reflector.4. A multi-spectral infrared radiation photodetector in accordance with claim 1, wherein the at least two bands of infrared radiation is two bands of infrared radiation.5. A multi-spectral infrared radiation photodetector in accordance with claim 1, wherein the at least two bands of infrared radiation is three bands of infrared radiation.6. A multi-spectral infrared radiation photodetector comprising:a plurality of elongate infrared radiation absorbing elements for absorbing at least two bands of infrared radiation, each of the plurality of elements having first and second opposite longitudinal surfaces, the at least two bands of infrared radiation incident upon the first surfaces of the plurality of elements; a plurality of electrically interconnected strips respectively being in electrical contact with and extending along the first surfaces of the plurality of elements; a bottom contact being in electrical contact with the second surfaces of the plurality of elements, the plurality of strips and the bottom contact to provide for current flow through the plurality of elements in a direction substantially transverse to an axis of the plurality of elements; and a reflector for reflecting the at least two bands of infrared radiation, the reflector being disposed on an opposite longitudinal surface of the bottom contact from the plurality of elements, wherein the plurality of elements, the plurality of strips, the bottom contact and the reflector comprise a diffractive resonant optical cavity, the diffractive cavity having a first period in a first direction for diffracting a first band of the at least two bands of infrared radiation and a second period in a second direction for diffracting a second band of the at least two bands of infrared radiation, the second band of infrared radiation different from the first band of infrared radiation, the second direction being substantially perpendicular to the first direction, and wherein a ratio between a photoresponse to each of the at least two bands of infrared radiation is a function of an external bias applied between the plurality of strips and the bottom contact. 7. A multi-spectral infrared radiation photodetector in accordance with claim 6, wherein the plurality of elements comprise multiple quantum well material selected from the group consisting of GaAs, AlGaAs, InGaAs, InP and combinations thereof.8. A multi-spectral infrared radiation photodetector in accordance with claim 6, wherein the reflector is either a metallic reflector or a Bragg reflector.9. A multi-spectral infrared radiation photodetector in accordance with claim 6, wherein the at least two bands of infrared radiation is two bands of infrared radiation.10. A multi-spectral infrared radiation photodetector in accordance with claim 6, wherein the at least two bands of infrared radiation is three bands of infrared radiation.11. A dual-band infrared radiation photodetector comprising:a plurality of elongate infrared radiation absorbing elements for absorbing first and second bands of infrared radiation, the second band of infrared radiation different from the first band of infrared radiation, each of the plurality of elements having first and second opposite longitudinal surfaces, the first and second bands of infrared radiation incident upon the first surfaces of the plurality of elements, the plurality of elements comprising multiple quantum well material including GaAs and AlGaAs; a plurality of electrically interconnected strips respectively being in electrical contact with and extending along the first surfaces of the plurality of elements; a bottom contact being in electrical contact with the second surfaces of the plurality of elements, the plurality of strips and the bottom contact to provide for current flow through the plurality of elements in a direction substantially transverse to an axis of the plurality of elements; and a metallic reflector for the first and second bands of infrared radiation, the reflector being disposed on an opposite longitudinal surface of the bottom contact from the plurality of elements, wherein the plurality of elements, the plurality of strips, the bottom contact and the reflector comprise a diffractive resonant optical cavity for the first and second bands of infrared radiation, and wherein a ratio between a photoresponse to the first and second bands of infrared radiation is a function of an external bias applied between the plurality of strips and the bottom contact. 12. A method of detecting first and second bands of infrared radiation comprising:generating a first spectral response curve of a photodetector with a first applied bias, the photodetector including: a plurality of elongate infrared absorbing elements for absorbing the first and second bands of infrared radiation, the plurality of elements having first and second opposing surfaces, the first and second bands of infrared radiation incident on the first surfaces of the plurality of elements; a plurality of electrically interconnected strips being in electrical contact with and extending along the first surfaces of the plurality of elements; a bottom electrical contact being in electrical contact with the second surfaces of the plurality of elements; and a reflector for the first and second bands of infrared radiation, the reflector being disposed on an opposite longitudinal surface of the bottom contact from the plurality of elements, wherein the plurality of elements, the plurality of strips, the bottom contact and the reflector comprise a diffractive resonant optical cavity for the first and second bands of infrared radiation, and wherein a ratio between a photoresponse to the first and second bands of infrared radiation is a function of an external bias applied between the plurality of strips and the bottom contact; generating a second spectral response curve of the photodetector at a second applied bias, the second applied bias different from the first applied bias; detecting infrared radiation at the first applied bias, thereby creating a first signal; detecting infrared radiation at the second applied bias, thereby creating a second signal; and deconvolving the first and second signals using the generated first and second spectral response curves, thereby creating a first band signal corresponding to the first band of infrared radiation and a second band signal corresponding to the second band of infrared radiation. 13. A method of detecting first and second bands of infrared radiation in accordance with claim 12, wherein a polarity of the first applied bias is opposite a polarity of the second applied bias.14. A multi-spectral infrared radiation imager including a plurality of photodetector pixel structures, each of the pixel structures comprising:a plurality of elongate infrared radiation absorbing elements for absorbing at least two bands of infrared radiation, each of the plurality of elements having first and second opposite longitudinal surfaces, the at least two bands of infrared radiation incident upon the first surfaces of the plurality of elements; a plurality of electrically interconnected strips respectively being in electrical contact with and extending along the first surfaces of the plurality of elements; a bottom electrical contact being in electrical contact with the second surfaces of the plurality of elements, the plurality of strips and the bottom contact to provide for current flow through the plurality of elements in a direction substantially transverse to an axis of the plurality of elements; and a reflector for the at least two bands of infrared radiation, the reflector being disposed on an opposite longitudinal surface of the bottom contact from the plurality of elements, wherein the plurality of elements, the plurality of strips, the bottom contact and the reflector comprise a diffractive resonant optical cavity for the at least two bands of infrared radiation, and wherein a ratio between a photoresponse to each of the at least two bands of infrared radiation is a function of an external bias applied between the plurality of strips and the bottom contact. 15. A multi-spectral infrared radiation imager in accordance with claim 14, wherein the plurality of elements of each of the pixel structures comprise multiple quantum well material selected from the group consisting of GaAs, AlGaAs, InGaAs, InP and combinations thereof.16. A multi-spectral infrared radiation imager in accordance with claim 14, wherein the reflector of each of the pixel structures is either a metallic reflector or a Bragg reflector.17. A multi-spectral infrared radiation imager in accordance with claim 14, wherein the at least two bands of infrared radiation is two bands of infrared radiation.18. A multi-spectral infrared radiation imager in accordance with claim 14, wherein the at least two bands of infrared radiation is three bands of infrared radiation.19. A multi-spectral infrared radiation imager in accordance with claim 14, wherein the multi-spectral infrared radiation imager is a one-dimensional multi-spectral infrared radiation imager.20. A multi-spectral infrared radiation imager in accordance with claim 14, wherein the multi-spectral infrared radiation imager is a two-dimensional multi-spectral infrared radiation imager.21. A multi-spectral infrared radiation imager including a plurality of photodetector pixel structures, each of the pixel structures comprising:a plurality of elongate infrared radiation absorbing elements for absorbing at least two bands of infrared radiation, each of the plurality of elements having first and second opposite longitudinal surfaces, the at least two bands of infrared radiation incident upon the first surfaces of the plurality of elements; a plurality of electrically interconnected strips respectively being in electrical contact with and extending along the first surfaces of the plurality of elements; a bottom electrical contact being in electrical contact with the second surfaces of the plurality of elements, the plurality of strips and the bottom contact to provide for current flow through the plurality of elements in a direction substantially transverse to an axis of the plurality of elements; and a reflector for reflecting the at least two bands of infrared radiation, the reflector being disposed on an opposite longitudinal surface of the bottom contact from the plurality of elements, wherein the plurality of elements, the plurality of strips, the bottom contact and the reflector comprise a diffractive resonant optical cavity, the diffractive cavity having a first period in a first direction for diffracting a first band of the at least two bands of infrared radiation and a second period in a second direction for diffracting a second band of the at least two bands of infrared radiation, the second band of infrared radiation different from the first band of infrared radiation, the second direction being substantially perpendicular to the first direction, and wherein a ratio between a photoresponse to each of the at least two bands of infrared radiation is a function of an external bias applied between the plurality of strips and the bottom contact. 22. A multi-spectral infrared radiation imager in accordance with claim 21, wherein the plurality of elements of each of the pixel structures comprise multiple quantum well material selected from the group consisting of GaAs, AlGaAs, InGaAs, InP and combinations thereof.23. A multi-spectral infrared radiation imager in accordance with claim 21, wherein the reflector of each of the pixel structures is either a metallic reflector or a Bragg reflector.24. A multi-spectral infrared radiation imager in accordance with claim 21, wherein the at least two bands of infrared radiation is two bands of infrared radiation.25. A multi-spectral infrared radiation imager in accordance with claim 21, wherein the at least two bands of infrared radiation is three bands of infrared radiation.26. A multi-spectral infrared radiation imager in accordance with claim 21, wherein the multi-spectral infrared radiation imager is a one-dimensional multi-spectral infrared radiation imager.27. A multi-spectral infrared radiation imager in accordance with claim 21, wherein the multi-spectral infrared radiation imager is a two-dimensional multi-spectral infrared radiation imager.28. A dual-band infrared radiation imager comprising:a plurality of photodetector pixel structures, each of the plurality of photodetector pixel structures including: a plurality of elongate infrared radiation absorbing elements for absorbing first and second bands of infrared radiation, the second band of infrared radiation different from the first band of infrared radiation, each of the plurality of elements having first and second opposite longitudinal surfaces, the first and second bands of infrared radiation incident upon the first surfaces of the plurality of elements, the plurality of elements comprising multiple quantum well material including GaAs and AlGaAs; a plurality of electrically interconnected strips respectively being in electrical contact with and extending along the first surfaces of the plurality of elements; a bottom electrical contact being in electrical contact with the second surfaces of the plurality of elements, the plurality of strips and the bottom contact to provide for current flow through the plurality of elements in a direction substantially transverse to an axis of the plurality of elements; and a metallic reflector for the first and second bands of infrared radiation, the reflector being disposed on an opposite longitudinal surface of the bottom contact from the plurality of elements, wherein the plurality of elements, the plurality of strips, the bottom contact and the reflector comprise a diffractive resonant optical cavity for the first and second bands of infrared radiation, and wherein a ratio between a photoresponse to the first and second bands of infrared radiation is a function of an external bias applied between the plurality of strips and the bottom contact, and a readout integrated circuit, the readout integrated circuit for sequentially applying first and second external biases between the plurality of strips and the bottom contact of each of the plurality of photodetector pixel structures, the readout integrated circuit for multiplexing the photoresponse of each of the plurality of photodetector pixel structures at the first and second external biases.